1. Field of the Invention
The present invention relates to a substrate treatment apparatus and a substrate treatment method for cleaning a peripheral portion of a substrate. Examples of the substrate to be treated include semiconductor wafers, glass substrates for liquid crystal display devices, substrates for plasma display devices, substrates for FED (Field Emission Display) devices, substrates for optical disks, substrates for magnetic disks, substrates for magneto-optical disks, substrates for photo masks, and substrates for photovoltaic cells.
2. Description of Related Art
In a semiconductor device production process, a thin metal film is formed on a device formation surface of a generally round substrate or a semiconductor wafer (hereinafter referred to simply as “wafer”), and then an etching process is often performed to etch away unnecessary portions of the thin metal film. Where the thin metal film is also formed on a peripheral portion of the wafer, for example, the metal is likely to contaminate a hand of a transport robot during the handling of the wafer by the transport robot, and the contamination is transferred to other wafers. Therefore, the unnecessary portions of the thin metal film are removed from the peripheral portion of the wafer.
A substrate treatment apparatus adapted to remove the thin metal film from the peripheral portion of the wafer includes, for example, a spin chuck which horizontally holds and rotates the wafer, and an etching liquid nozzle which supplies an etching liquid to a lower surface of the wafer. The wafer is held by the spin chuck with its front surface (formed with the device formation region) facing up. A center axis nozzle inserted through a rotation shaft of the spin chuck is used as the etching liquid nozzle. The center axis nozzle has a spout provided at an upper end thereof in opposed relation to a center portion of the lower surface of the wafer held by the spin chuck. When the etching liquid spouted from the spout reaches the lower surface of the wafer, the etching liquid receives a centrifugal force to spread outward radially about a rotation center, and flows around to an upper surface of the wafer from a peripheral edge of the wafer. Thus, the unnecessary portions are etched away from a peripheral portion of the upper surface of the wafer. The etching process (so-called bevel etching process) is performed on a region of the peripheral portion of the upper surface of the wafer having a predetermined width (e.g., 0.5 to 1.5 mm) by controlling the flow rate of the etching liquid spouted from the etching liquid nozzle and the rotation speed of the spin chuck (see US2003/196683A1).
With the aforementioned arrangement, however, it is difficult to precisely control the width (treatment width) of the region of the upper surface of the wafer from which the thin metal film is removed.
Where the lower surface of the wafer (or a surface of the thin film formed on the lower surface of the wafer) has in-plane variations in hydrophilicity, the etching liquid is liable to move toward the lower surface peripheral portion of the wafer along higher hydrophilicity regions of the lower surface. Therefore, the etching liquid does not necessarily spread uniformly but radially linearly, so that the etching liquid is supplied at different flow rates to the peripheral portion of the wafer. Therefore, the etching liquid flow-around amount varies over the peripheral portion of the wafer.
Further, the flow rate of the etching liquid spouted from the etching liquid nozzle is liable to be unstable at the start of the spouting of the etching liquid. Even after a lapse of a certain period of time from the start of the spouting of the etching liquid, the flow rate of the etching liquid spouted from the etching liquid nozzle is liable to be momentarily changed due to pulsation of a pump. If the flow rate of the etching liquid spouted from the etching liquid nozzle is changed during the etching process, the flow rate of the etching liquid supplied to the peripheral portion of the wafer is also changed. Therefore, the amount of the etching liquid flowing around to the upper surface of the wafer is liable to differ from a desired flow-around amount.
The same problem occurs not only in the bevel etching process but also when the upper surface peripheral portion of the wafer is treated (cleaned) with a chemical agent such as a cleaning agent.